VOLTAGEDROPCALCULATOR
Quick Field Planning Tool

Maximum Circuit LengthCalculator

Find the maximum one-way circuit length that stays within a selected voltage-drop limit for a given conductor and load.

Find the longest practical one-way run before a selected conductor exceeds your voltage-drop target. The layout is intentionally thumb-friendly for fast jobsite checks on a phone, but the calculation still uses the standard conductor-resistance method electricians and engineers expect.

Quick Inputs

Large controls for one-handed mobile use

Length Result

Fast field check

Maximum one-way length
57 ft
Based on 12 copper and a 3% drop target.
Allowable drop
3.60 V
Effective resistance
1.9800
Ohms / 1000 ft
Planned run check

At 100 ft one-way, estimated drop is 6.34 V (5.28%).

43 ft over the selected drop limit.

Engineering note

Single-phase result is a quick planning check using conductor resistance at 75 C.

How to use this tool
Pick the system type, voltage, current, and conductor you actually expect to install.
Use the result as the longest one-way route that stays at or below the selected drop percentage.
If the planned run fails, reduce current, increase conductor size, add parallel sets, or move into the full AC/DC calculators.
Related calculators and references
AC Voltage Drop Calculator

Use the full AC workflow when power factor, impedance, or conduit effects matter.

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DC Voltage Drop Calculator

Check exact DC circuit drop once you know the real installed length.

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Wire Size Calculator

Move from a length limit to a conductor recommendation when the run is already fixed.

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Wire Tables

Review conductor resistance and ampacity data behind the quick field calculation.

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NEC Standards

Confirm design targets and code context before finalizing feeder and branch-circuit work.

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